We consider a status update system consisting of two independent sources, one server, and one sink. The packets of different sources are generated according to the Poisson process and the packets are served according to an exponentially distributed service time. We consider the following packet management policy. When the system is empty, any arriving packet immediately enters the server; when the server is busy, a packet of a source waiting in the queue is replaced if a new packet of the same source arrives. We derive the average age of information (AoI) of the considered M/M/1 queueing model by using the stochastic hybrid systems (SHS) technique. Numerical results are provided to show the effectiveness of the proposed policy.
In applications of remote sensing, estimation, and control, timely communication is not always ensured by high-rate communication. Oftentimes, it is observed that as the capacity of a system is approached, delay increases significantly and so does age of information – a metric recently proposed to capture freshness and timeliness of information. This work proposes distributed age-efficient transmission policies for random access channels with M transmitters and provides asymptotic results for the age of information as M → ∞. Slotted Aloha-type algorithms are shown to be asymptotically age-optimal for arrival rates below 1/eM and far from optimal for larger arrival rates. For larger arrival rates, novel distributed age-based policies are proposed that benefit from the availability of fresh packets to reduce age of information. For arrival rates θ, θ =1/o(M), the proposed algorithms provide a multiplicative gain factor of at least two compared to the state-of-the-art schemes. We conclude that, as opposed to the common practice, it is beneficial to increase the sampling rate (and hence the arrival rate) and transmit packets selectively based on their “age-gains”, a notion defined in the paper.
In this paper, we consider a status updating system where updates are generated at a constant rate at $K$ sources and sent to the corresponding recipients through a broadcast channel. We assume that perfect channel state information (CSI) is available at the transmitter before each transmission, and the additive noise is negligible at the receivers. Under various assumptions on the number of antennas at the transmitter and the size of updates, our object is to design precoding and transmission scheduling schemes for the minimization of the summed time-average Age of Information (AoI) at the recipients. We show that when the transmitter has a single antenna, precoding is unnecessary, and the optimal policy is to update each recipient in a greedy round-robin fashion. When the transmitter has multiple antennas, updating with round-robin precoding is age-optimal.
The ever-increasing needs of supporting real-time applications have spurred a considerable number of studies on minimizing Age-of-Information (AoI), a new metric characterizing the data freshness of the system. This work revisits and significantly strengthens the seminal results of Sun et al. on the following fronts: (i) The optimal waiting policy is generalized from the 1-way delay to the 2-way delay setting; (ii) A new way of computing the optimal policy with quadratic convergence rate, an order-of-magnitude improvement over the state-of-the-art bisection methods; and (iii) A new low-complexity adaptive online algorithm that provably converges to the optimal policy without knowing the exact delay distribution, a sharp departure from the existing AoI algorithms. Contribution (iii) is especially important in practice since the delay distribution can sometimes be hard to know in advance and may change over time. Simulation results in various settings are consistent with the theoretic findings.